magnum/src/Magnum/Math/StrictWeakOrdering.h

#ifndef Magnum_Math_StrictWeakOrdering_h
#define Magnum_Math_StrictWeakOrdering_h
/*
    This file is part of Magnum.

    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019,
                2020, 2021, 2022 Vladimír Vondruš <mosra@centrum.cz>
    Copyright © 2018 Borislav Stanimirov <b.stanimirov@abv.bg>

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.
*/

/** @file
 * @brief Struct @ref Magnum::Math::StrictWeakOrdering
 */

namespace Magnum { namespace Math {

namespace Implementation {

template<class T> struct StrictWeakOrdering { /* Specialized for supported types */
    bool operator()(const T& a, const T& b) const {
        return a < b;
    }
};

}

/**
@brief A functor which implements strict weak ordering

A strict weak ordering enables a comparison operator between two elements of a
set. With it an ordering can be achieved between the elements. This is useful
mainly for interoperability with ordering containers from the C++ standard
library, like @ref std::map and @link std::set @endlink:

@snippet MagnumMath.cpp StrictWeakOrdering

The implementation is done for all types in the @ref Math library, check the
source for defails if you want to create an implementation for your own types.
 */
struct StrictWeakOrdering {
    /**
     * @brief Compares two items
     *
     * Returns @cpp true @ce if @p a is less than @p b, returns @cpp false @ce
     * if @p a is equivalent to @p b or greater. For scalar types this is
     * equivalent to @cpp operator< @ce.
     */
    template<class T> bool operator()(const T& a, const T& b) const {
        /* Instantiate a specialization of Implementation::StrictWeakOrdering.
           If users want to enable this for their own types, they must create
           a specialization of Magnum::Math::Implementation::StrictWeakOrdering
           for them. */
        Implementation::StrictWeakOrdering<T> o;
        return o(a, b);
    }
};

}}

#endif